In scuba diving, for instance, a supply of air, or of an air-oxygen mixture, is typically fed to a mouthpiece of the scuba diver from a high-pressure tank. Enroute to the diver, the air passes from a primary or first-stage pressure-reducing regulator to a second-stage regulator which, in turn, supplies the mixture to the mouthpiece, namely, when pressure within the regulator is diminished upon the diver's inhalation.
Second-stage regulators typically have an inlet chamber connected to an outlet of the first-stage regulator, and an outlet chamber connected to the mouthpiece of the user. The outlet chamber is separated from the external environment by an elastically deformable diaphragm. The diaphragm is joined via a lever to a poppet which closes a passage between the inlet and outlet chambers.
Through appropriate calibration of the first-stage regulator, the pressure inside the inlet chamber is maintained relatively constant at approximately ten bars as the pressure in the tank varies. When the user does not breathe, his or her lungs, the mouthpiece, the outlet chamber and the outside environment are generally at the same pressure. When the user inhales, on the other hand, a vacuum is created in the outlet chamber, and the diaphragm bends toward the interior of the chamber, moving the poppet, which normally closes the passage between the inlet and outlet chambers, to an open or operative position.
Opening the passage between the inlet and outlet chambers causes excess pressure in the outlet chamber, such that the diaphragm returns to a stowed or resting position, in turn, moving the lever and returning the poppet to a starting or stowed position at which the passage between the inlet and outlet chambers is again in a closed position.
In this manner, the vacuum created when the user inhales effectively controls movement of the interconnected mechanical actuating members, i.e., the diaphragm, lever and poppet. The exertion or energy required by the user, upon inhalation, must also account for the energy dissipated by friction between the mechanical members.